1. Field of the Invention
The present invention relates to an image processing apparatus to conduct an on-screen display operation in which an image is superimposed on an image in a screen.
2. Description of the Related Art
Image pickup devices such as a digital still camera and a digital movie camera including a solid-state image pickup device, for example, a charge-coupled device (CCD) have been put to business uses and other general uses. In such an image pickup device, a technique called “on-screen display (OSD)” is employed. That is, while displaying image data sent from an image data source or the like as a main screen image on a screen, another secondary information, for example, character information is displayed in a minimized size on the same screen. Using an image processing apparatus having the OSD function, an image of nature, character information, and/or a mobile picture can be freely displayed.
However, the image processing apparatus having the OSD function is attended with a problem. That is, OSD data is frequently read from an memory and hence occupies most of a bus band of an image memory.
Since the memory bus band is limited, the OSD data and the number of screen images to be display are also restricted. This leads to reduction of frames in the displayed picture and deterioration of display resolution, and hence picture quality is deteriorated. When frequency of OSD data accesses becomes greater, there possibly occurs a case in which the band necessary to communicate data between the memory and a central processing unit (CPU) cannot be sufficiently reserved.
To simply solve the problem, it is only necessary to increase an access speed of the memory. However, since power consumption of the memory increases in this case, a problem of “electromagnetic interference (EMI)” takes place.
Therefore, to smoothly conduct image processing, it is necessary to reduce the number of OSD data accesses.